All

We develop a geometric framework to describe the thermodynamics of
microscopic heat engines driven by slow periodic temperature variations and
modulations of a mechanical control parameter. Covering both the classical and
the quantum regime, our approach reveals a universal trade-off relation between
efficiency and power that follows solely from geometric arguments and holds for
any thermodynamically consistent microdynamics. Focusing on Lindblad dynamics,

We investigate the conditions under which an uncontrollable background
processes may be harnessed by an agent to perform a task that would otherwise
be impossible within their operational framework. This situation can be
understood from the perspective of resource theory: rather than harnessing
'useful' quantum states to perform tasks, we propose a resource theory of
quantum processes across multiple points in time. Uncontrollable background
processes fulfil the role of resources, and a new set of objects called

We present an elementary, general, and semi-quantitative description of
relaxation to gaussian and generalized Gibbs states in lattice models of
fermions or bosons with quadratic hamiltonians. Our arguments apply to
arbitrary initial states that satisfy a mild condition on clustering of
correlations. We also show that similar arguments can be used to understand
relaxation (or its absence) in systems with time-dependent quadratic
hamiltonians, and provide a semi-quantitative description of relaxation in

A novel protocol of interrogation based on coherent population trapping in an
N-level scheme atomic system leads to dark resonances involving three different
photons. An ensemble of several hundreds of radiofrequency-trapped ions is
probed by three lasers simultaneously locked onto the same optical frequency
comb, resulting in high-contrast spectral lines referenced to an atomic
transition in the THz domain. We discuss the cause of uncertainties and
limitations for this method and show that reaching a sub-kHz resolution is

The time-dependent pseudo-Hermitian formulation of quantum mechanics allows
to study open system dynamics in analogy to Hermitian quantum systems. In this
setting, we show that the notion of holonomic quantum computation can equally
be formulated for pseudo-Hermitian systems. Starting from a degenerate
pseudo-Hermitian Hamiltonian we show that, in the adiabatic limit, a
non-Abelian geometric phase emerges which realizes a pseudounitary quantum
gate. We illustrate our findings by studying a pseudo-Hermitian gain/loss

Brillouin scattering has applications ranging from signal processing, sensing
and microscopy, to quantum information and fundamental science. Most of these
applications rely on the electrostrictive interaction between light and
phonons. Here we show that in liquids optically-induced surface deformations
can provide an alternative and far stronger interaction. This allows the
demonstration of ultralow threshold Brillouin lasing and strong phonon-mediated
optical coupling for the first time. This form of strong coupling is a key

We identify significant quantum many-body effects, robust to position
fluctuations and strong dipole--dipole interactions, in the forward light
scattering from planar arrays and uniform-density disks of cold atoms, by
comparing stochastic electrodynamics simulations of a quantum master equation
and of a semiclassical model that neglects quantum fluctuations. Quantum
effects are pronounced at high atomic densities with the light close to
saturation intensity, and especially at subradiant resonances. We find an

A wide range of fundamental machine learning tasks that are addressed by the
maximum a posteriori estimation can be reduced to a general minimum conical
hull problem. The best-known solution to tackle general minimum conical hull
problems is the divide-and-conquer anchoring learning scheme (DCA), whose
runtime complexity is polynomial in size. However, big data is pushing these
polynomial algorithms to their performance limits. In this paper, we propose a

Any measurement is intended to provide information on a system, namely
knowledge about its state. However, we learn from quantum theory that it is
generally impossible to extract information without disturbing the state of the
system or its correlations with other systems. In this paper we address the
issue of the interplay between information and disturbance for a general
operational probabilistic theory. The traditional notion of disturbance
considers the fate of the system state after the measurement. However, the fact

In a conventional atomic interferometer employing $N$ atoms, the phase
sensitivity is at the standard quantum limit: $1/\sqrt{N}$. Using
spin-squeezing, the sensitivity can be increased, either by lowering the
quantum noise or via phase amplification, or a combination thereof. Here, we
show how to increase the sensitivity, to the Heisenberg limit of $1/N$, while
increasing the quantum noise by $\sqrt{N}$, thereby suppressing by the same
factor the effect of excess noise. The proposed protocol makes use of a

Pages